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A337399
Numbers k such that sigma(k) is a Zumkeller number (A083207).
1
5, 6, 11, 12, 14, 15, 19, 20, 23, 24, 26, 27, 28, 29, 33, 34, 35, 38, 39, 40, 41, 42, 44, 45, 47, 53, 54, 56, 57, 58, 59, 60, 62, 63, 65, 68, 69, 74, 76, 77, 78, 79, 80, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 95, 96, 99, 101, 102, 103
OFFSET
1,1
COMMENTS
Sequence contains many semiprimes of the form p(m)*p(m+1). Only 6 of the first 200 semiprimes of this form are not terms, those where m is in {15, 37, 99, 100, 121, 197}.
LINKS
MATHEMATICA
zQ[n_]:=Module[{d=Divisors[n], t, ds, x}, ds=Plus@@d; If[Mod[ds, 2]>0, False, t=CoefficientList[Product[1+x^i, {i, d}], x]; t[[1+ds/2]]>0]]; Select[Range[200], zQ[DivisorSigma[1, #]]&] (* code by T. D. Noe at A083207 *)
CROSSREFS
Cf. A000203, A083207, A320518 (subsequence).
Sequence in context: A287265 A120517 A246395 * A139071 A092296 A046608
KEYWORD
nonn,easy
AUTHOR
Ivan N. Ianakiev, Aug 26 2020
STATUS
approved